The present invention relates to a method and an apparatus therefor for generating and collecting ultra-fine particles by means of gas evaporation technique, which method and apparatus are for obtaining organic ultra-fine particles such as organic photoconductor ultra-fine particles used for manufacturing an electrophotographic photoreceptor. The invention relates particularly to a method for generating ultra-fine particles through a gas evaporation method which is a method of evaporation in a gas atmosphere and for collecting them and to an apparatus therefor. The method of evaporation in a gas atmosphere is one wherein various kinds of substances are heated, evaporated and sublimated in the atmosphere of inactive gas or inert gas contained in a vacuum container, and a molecule in vapor thus generated is cooled down gradually while it collides with a molecule of the inactive gas, and molecules cohere to form an ultra-fine particle which is then collected.
An electrophotographic photoreceptor has basic structure wherein a light-sensitive layer is formed on an electrically conductive substrate. As a photoconductive substance for forming the light-sensitive layer, selenium has generally been used, and other substances known as inorganic photoconductive substance include cadmium sulfide and zinc oxide.
Recently, however, it is attempted, by using organic photoconductive substance, to improve the layer-forming efficiency and to raise productivity by manufacturing through a coating process. Further, the usage of an organic photoconductive substance offers an advantage in that the color sensitivity can be controlled freely if sensitizers for dyes and the pigments used are selected. As organic photoconductive substance, there has been known poly-N-vinylcarbazole and 2.5-bis (P-diethylaminophenyl)-1,3,4-oxyadiazole.
The organic photoconductive substance functions in the state of ultra-fine particles dispersed in a binder.
Recently, on the other hand, studies on an ultra-fine particle in a size of .mu.m order or .ANG. order have been made. Such an ultra-fine particle is generated, which shows higher activity when its specific surface area increases.
In this case, a method of evaporation in a gas atmosphere among others is attracting public attention. This method has tended to be the subject for the study only for obtaining ultra-fine particles of inorganic material or metallic material, but the study has also been made to obtain ultra-fine particles of an organic substance as is disclosed on pages 44-49 in `Functional Materials` of June issue in 1987.
In any case, ultra-fine particles evaporated in a gas atmosphere and deposited on a particle-receiving member have hitherto been collected as shown in FIGS. 17 and 18.
Namely, in the first method, there is provided in a vacuum chamber (not shown), as shown in FIG. 17 (a), container 50 which contains evaporative material M, flat or curved plate 51 that serves as a particle-receiving member, when necessary, recovery container 52 that receives falling particles, and container 50 in which evaporative materials are heated for evaporation under a condition in which the vacuum chamber contains inactive gas and is decompressed to a vacuum, and evaporated materials thus generated are caused to be deposited on aforesaid curved plate 51, and then, as shown in FIG. 17 (b), a layer of material deposited on the surface of curved plate 51 is scraped off by brush 53 or the like to be collected into recovery box 54.
In the second method, evaporative material M is caused to be deposited, in the evaporation embodiment identical no that in the first method, on the surface of web 60 while plastic web 60, which serves as a particle-receiving member, is supplied from reel 61 and is taken up by reel 62 as shown in FIG. 18 (b), and for collecting evaporated material, evaporative material M deposited on the surface of web 60 is scraped off with a brush or the like to be collected into recovery box 54 while web 60 is supplied from reel 62 which once took up web 60.
On the other hand, there is also known the recovery method wherein a web on which evaporative materials are deposited is subjected to supersonic treatment in a solvent for recovery.
However, the aforesaid first method is of a type of a batch system. With the lapse of time, therefore, powder substances are deposited causing gradual lamenation of the recovery plate until the thickness of the lamination reaches a certain value. Therefore, even if the recovery plate is cooled down, the laminated powder layer receives radiant heat emitted from the evaporation source, resulting in remarkable thermal deterioration, especially when the powder is less heat-resistant. Further, in the case of a material having the characteristic of needle-like growth, particles grow to be a cobweb shape (a shape of a filament) and thereby, it is not possible to obtain the target ultra-fine particles. In addition to that, an excessive amount of particles drop during course of lamination, causing the recovery to be difficult. Further, due to the two steps of deposition and recovery, the working efficiency is poor, which is identical to the second method explained below.
In the second method, on the other hand, deposited materials are scraped off between the reels in addition to that the number of steps is two. Therefore, the scraping is unstable and difficult due to the plastic web to which the brush can not be applied with sufficient pressure. Therefore, the efficiency of recovery and the rate of recovery are poor.
On the other hand, the method of recovery wherein a web on which evaporative materials are deposited is subjected to supersonic treatment in a solvent has disadvantages that the separation of evaporative materials from the solvent takes time and labor and a drying step for eliminating solvent is needed.